This invention relates to terpolymers and more particularly to terpolymers of ethylene, vinyl acetate and isobutylene useful as pour point depressants and/or flow improvers in distillate fuel oils.
The serious concern over supplies of petroleum has led to increased interest in diesel engines for passenger automobiles because of their proven economy in operation. Distillate oil fuels for automotive use must be made suitable, in cold weather, for uninterrupted service. Pour point depressants to promote cold temperature pour are added by the producer of the distillate or may be sold in automobile supply outlets, for direct addition by the consumer. In either case, a clear pour point additive is desirable from a marketing standpoint. Often a multiadditive system is prepared which combines pour point effectiveness with other functions such as corrosion inhibition and detergency to reduce nozzle deposits.
The use of ethylene-vinyl acetate copolymers to improve the low temperature pour characteristics of distillate oils has long been known. U.S. Pat. No. 3,048,479 describes the use of ethylene-vinyl acetate copolymers containing about 20 percent by weight vinyl acetate to improve the pour of distillate fuels. Such polymers are prepared in a solvent such as benzene at low pressures of around 800 psi using ditertiary butyl peroxide. U.S. Pat. No. 3,627,838 describes a process for manufacturing an ethylene-vinyl acetate copolymer containing 28 to 60 weight percent vinyl acetate where the monomers are reacted at a temperature of 280.degree. F. to 340.degree. F. under a pressure of 700 to 2000 psi in a solvent with azo compounds or peroxides such as ditertiary butyl peroxide. Similar processes are described in U.S. Pat. No. 3,126,364 and U.S. Pat. No. 3,254,063. A further modification in the use of ethylene-vinyl acetate copolymers as pour depressants is shown in U.S. Pat. No. 3,961,916 wherein two synthetic ethylene-vinyl acetate copolymers differing by at least 5 weight percent vinyl ester content are separately prepared and blended to produce a pour depressent additive.
A slightly different approach is disclosed in U.S. Pat. No. 4,087,255 which describes the preparation of ethylene-vinyl acetate copolymers for use as pour point depressants by reacting the monomers in an inert solvent at relatively low temperatures (70.degree. to 120.degree. C.) and pressures of 700 to 3000 psig. Polymers produced in this manner, having a molecular weight around 1000-2900, show reduced branching characterized by 2-methyl side branches per 100 methylene groups.
Other patents disclose the use of terpolymers of ethylene, vinyl acetate and monolefinically unsaturated polymerizable monomers for use as pour point depressants. For example, U.S. Pat. No. 3,467,597 discloses terpolymers of ethylene, vinyl acetate and butylenes. U.S. Pat. No. 3,638,349 discloses copolymers of ethylene and vinyl acetate wherein up to 20% of the copolymer can be other polymerizable unsaturated monomers. U.S. Pat. No. 4,178,950 discloses terpolyumers of ethylenevinyl acetate-butylene prepared by solution polymerization and of a number average molecular weight of about 5,000 to about 80,000, preferably 12,000 to about 60,000.
Improved pour point depressants having better clarity compared to presently used EVA copolymers, which are hazy at room temperature, and which suffer no adverse effects insofar as compatibility and response in distillate fuels are very much desired.